Neutron star matter equation of state including d^*-hexaquark degrees of freedom

¹ Department of Physics, University of York, Heslington, York Y010 5DD, UK
e-mail: alessandro.pastore@york.ac.uk
² Department of Physics, Imperial College London, London SW7 2AZ, UK
³ INFN Sezione di Catania, Dipartimento di Fisica “Ettore Majorana”, Università di Catania, Via Santa Sofia 64, 95123 Catania, Italy

Received: 16 February 2020
Accepted: 12 April 2020

Abstract

We present the extension of a previous study where, assuming a simple free bosonic gas supplemented with a relativistic mean-field model to describe the pure nucleonic part of the equation of state, we studied the consequences that the first non-trivial hexaquark d^*(2380) could have on the properties of neutron stars. Compared to that exploratory work, we employ a standard non-linear Walecka model including additional terms that describe the interaction of the d^*(2380) di-baryon with the other particles of the system through the exchange of σ- and ω-meson fields. Our results show that the presence of the d^*(2380) leads to maximum masses compatible with recent observations of ∼2 M_⊙ millisecond pulsars if the interaction of the d^*(2380) is slightly repulsive or the d^*(2380) does not interact at all. An attractive interaction makes the equation of state too soft to be able to support a 2 M_⊙ neutron star whereas an extremely repulsive one induces the collapse of the neutron star into a black hole as soon as the d^*(2380) appears.